Don't default to default RPC if user input undefined/null RPC url

[tonisives]

Check existing issues

• I checked there isn't already an issue for the bug I encountered.

Viem Version

2.23.2

Current Behavior

/**
 * @description Creates a HTTP transport that connects to a JSON-RPC API.
 */
export function http(
  /** URL of the JSON-RPC API. Defaults to the chain's public RPC URL. */
  url?: string | undefined,
  config: HttpTransportConfig = {},
): HttpTransport {
  const {
    batch,
    fetchOptions,
    key = 'http',
    methods,
    name = 'HTTP JSON-RPC',
    onFetchRequest,
    onFetchResponse,
    retryDelay,
  } = config
  return ({ chain, retryCount: retryCount_, timeout: timeout_ }) => {
    const { batchSize = 1000, wait = 0 } =
      typeof batch === 'object' ? batch : {}
    const retryCount = config.retryCount ?? retryCount_
    const timeout = timeout_ ?? config.timeout ?? 10_000
    const url_ = url || chain?.rpcUrls.default.http[0]

I debugged multiple hours about why my service was successful on local, but failed in Docker. It failed in Docker, because I had undefined env values, and viem defaulted to eth.merkle.io as RPC. Then, the merkle.io failed with 429.

I had no idea why this was happening, and had to search through viem source code to find this custom logic.

Expected Behavior

User input (undefined RPC url) should be honored. Viem should not try to recover from this and suggest it's own RPC url. Users want to know immediately when they input wrong values, so they can fix their environment.

Steps To Reproduce

No response

Link to Minimal Reproducible Example

No response

Anything else?

No response

[jxom]

We can keep this in mind for v3.